Refactor Context::run() method

boa_engine/src/builtins/function/mod.rs

@@ -775,6 +775,7 @@ impl BuiltInFunctionObject {
             let code = FunctionCompiler::new()
                 .name(Sym::ANONYMOUS)
                 .generator(true)
+                .r#async(r#async)
                 .compile(
                     &FormalParameterList::default(),
                     &FunctionBody::default(),
@@ -793,12 +794,15 @@ impl BuiltInFunctionObject {
 
             Ok(function_object)
         } else {
-            let code = FunctionCompiler::new().name(Sym::ANONYMOUS).compile(
-                &FormalParameterList::default(),
-                &FunctionBody::default(),
-                context.realm().environment().compile_env(),
-                context,
-            );
+            let code = FunctionCompiler::new()
+                .r#async(r#async)
+                .name(Sym::ANONYMOUS)
+                .compile(
+                    &FormalParameterList::default(),
+                    &FunctionBody::default(),
+                    context.realm().environment().compile_env(),
+                    context,
+                );
 
             let environments = context.vm.environments.pop_to_global();
             let function_object =

boa_engine/src/bytecompiler/declarations.rs

@@ -1010,11 +1010,10 @@ impl ByteCompiler<'_, '_> {
         if !formals.has_rest_parameter() {
             self.emit_opcode(Opcode::RestParameterPop);
         }
+
         if generator {
-            self.emit_opcode(Opcode::PushUndefined);
-            // Don't need to use `AsyncGeneratorYield` since
-            // we just want to stop the execution of the generator.
-            self.emit_opcode(Opcode::GeneratorYield);
+            self.emit_opcode(Opcode::Generator);
+            self.emit_u8(self.in_async().into());
             self.emit_opcode(Opcode::Pop);
         }
 

boa_engine/src/bytecompiler/function.rs

@@ -4,7 +4,7 @@ use crate::{
     builtins::function::ThisMode,
     bytecompiler::ByteCompiler,
     environments::CompileTimeEnvironment,
-    vm::{CodeBlock, CodeBlockFlags},
+    vm::{CodeBlock, CodeBlockFlags, Opcode},
     Context,
 };
 use boa_ast::function::{FormalParameterList, FunctionBody};
@@ -120,6 +120,31 @@ impl FunctionCompiler {
         // Function environment
         compiler.push_compile_environment(true);
 
+        // Taken from:
+        //  - 15.9.3 Runtime Semantics: EvaluateAsyncConciseBody: <https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncconcisebody>
+        //  - 15.8.4 Runtime Semantics: EvaluateAsyncFunctionBody: <https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncfunctionbody>
+        //
+        // Note: In `EvaluateAsyncGeneratorBody` unlike the async non-generator functions we don't handle exceptions thrown by
+        // `FunctionDeclarationInstantiation` (so they are propagated).
+        //
+        // See: 15.6.2 Runtime Semantics: EvaluateAsyncGeneratorBody: https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncgeneratorbody
+        if compiler.in_async() && !compiler.in_generator() {
+            // 1. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+            //
+            // Note: If the promise capability is already set, then we do nothing.
+            // This is a deviation from the spec, but it allows to set the promise capability by
+            // ExecuteAsyncModule ( module ): <https://tc39.es/ecma262/#sec-execute-async-module>
+            compiler.emit_opcode(Opcode::CreatePromiseCapability);
+
+            // 2. Let declResult be Completion(FunctionDeclarationInstantiation(functionObject, argumentsList)).
+            //
+            // Note: We push an exception handler so we catch exceptions that are thrown by the
+            // `FunctionDeclarationInstantiation` abstract function.
+            //
+            // Patched in `ByteCompiler::finish()`.
+            compiler.async_handler = Some(compiler.push_handler());
+        }
+
         let (env_label, additional_env) = compiler.function_declaration_instantiation(
             body,
             parameters,
@@ -128,6 +153,18 @@ impl FunctionCompiler {
             self.generator,
         );
 
+        // Taken from:
+        // - 27.6.3.2 AsyncGeneratorStart ( generator, generatorBody ): <https://tc39.es/ecma262/#sec-asyncgeneratorstart>
+        //
+        // Note: We do handle exceptions thrown by generator body in `AsyncGeneratorStart`.
+        if compiler.in_generator() {
+            assert!(compiler.async_handler.is_none());
+            if compiler.in_async() {
+                // Patched in `ByteCompiler::finish()`.
+                compiler.async_handler = Some(compiler.push_handler());
+            }
+        }
+
         compiler.compile_statement_list(body.statements(), false, false);
 
         if let Some(env_labels) = env_label {

boa_engine/src/bytecompiler/jump_control.rs

@@ -122,7 +122,23 @@ impl JumpRecord {
         match self.kind {
             JumpRecordKind::Break => compiler.patch_jump(self.label),
             JumpRecordKind::Continue => compiler.patch_jump_with_target(self.label, start_address),
-            JumpRecordKind::Return => compiler.emit_opcode(Opcode::Return),
+            JumpRecordKind::Return => {
+                match (compiler.in_async(), compiler.in_generator()) {
+                    // Taken from:
+                    //  - 27.6.3.2 AsyncGeneratorStart ( generator, generatorBody ): https://tc39.es/ecma262/#sec-asyncgeneratorstart
+                    //
+                    // Note: If we are returning we have to close the async generator function.
+                    (true, true) => compiler.emit_opcode(Opcode::AsyncGeneratorClose),
+
+                    // Taken from:
+                    //  - 27.7.5.2 AsyncBlockStart ( promiseCapability, asyncBody, asyncContext ): <https://tc39.es/ecma262/#sec-asyncblockstart>
+                    //
+                    // Note: If there is promise capability resolve or reject it based on pending exception.
+                    (true, false) => compiler.emit_opcode(Opcode::CompletePromiseCapability),
+                    (_, _) => {}
+                }
+                compiler.emit_opcode(Opcode::Return);
+            }
         }
     }
 }

boa_engine/src/bytecompiler/mod.rs

@@ -255,8 +255,13 @@ pub struct ByteCompiler<'ctx, 'host> {
     names_map: FxHashMap<Identifier, u32>,
     bindings_map: FxHashMap<BindingLocator, u32>,
     jump_info: Vec<JumpControlInfo>,
-    in_async: bool,
+    pub(crate) in_async: bool,
     in_generator: bool,
+
+    /// Used to handle exception throws that escape the async function types.
+    ///
+    /// Async functions and async generator functions, need to be closed and resolved.
+    pub(crate) async_handler: Option<u32>,
     json_parse: bool,
 
     // TODO: remove when we separate scripts from the context
@@ -305,6 +310,7 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
             jump_info: Vec::new(),
             in_async: false,
             in_generator: false,
+            async_handler: None,
             json_parse,
             current_environment,
             context,
@@ -1410,7 +1416,10 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
     #[allow(clippy::missing_const_for_fn)]
     pub fn finish(mut self) -> CodeBlock {
         // Push return at the end of the function compilation.
-        self.emit_opcode(Opcode::Return);
+        if let Some(async_handler) = self.async_handler {
+            self.patch_handler(async_handler);
+        }
+        self.r#return();
 
         let name = self
             .context

boa_engine/src/environments/runtime/mod.rs

@@ -78,6 +78,18 @@ impl EnvironmentStack {
         self.stack[0] = Environment::Declarative(global);
     }
 
+    /// Gets the current global environment.
+    pub(crate) fn global(&self) -> Gc<DeclarativeEnvironment> {
+        let env = self.stack[0].clone();
+
+        match env {
+            Environment::Declarative(ref env) => env.clone(),
+            Environment::Object(_) => {
+                unreachable!("first environment should be the global environment")
+            }
+        }
+    }
+
     /// Extends the length of the next outer function environment to the number of compiled bindings.
     ///
     /// This is only useful when compiled bindings are added after the initial compilation (eval).

boa_engine/src/module/source.rs

@@ -1414,6 +1414,10 @@ impl SourceTextModule {
 
         let mut compiler =
             ByteCompiler::new(Sym::MAIN, true, false, module_compile_env.clone(), context);
+
+        compiler.in_async = true;
+        compiler.async_handler = Some(compiler.push_handler());
+
         let mut imports = Vec::new();
 
         let (codeblock, functions) = {